1. Field of the Invention
This invention relates generally to insulation of a roof for an industrial oven.
2. Background Art
Industrial ovens often operate at temperatures near or above the melting point of most metal; for example, coking ovens can operate at temperatures approaching 1300° C. (about 2400° F.). Even when the product is required to be heated to temperatures below the melting point of the metal structure, metal becomes weak and subject to increased oxidation at elevated temperatures. Industrial ovens, such as industrial tunnel ovens, require insulation to efficiently retain heat within the oven and to prevent heat related damage to structural elements of the oven and to surrounding facility structure, equipment and personnel. In some prior industrial ovens the insulation has been provided with structural refractory brick. Refractory brick is expensive and difficult to support when constructing roofs and particularly for large area roofs such as those found in industrial tunnel ovens.
In recent years the insulation has been provided in some industrial ovens with lightweight, high temperature insulation materials such as fiberglass batting, ceramic fiber mat, or ceramic fiber blanket materials. Such lightweight materials in sheet form are sufficiently light to be supported from a roof; however, such materials do not generally have sufficient mechanical strength against sagging when extended across large areas. The typical oven has a metal roof, sometimes made of high temperature heat resistant steel. The highest temperature metal materials available at a reasonable cost for large scale construction are not capable of withstanding the internal oven temperature. Sheets of the fibrous insulating material are generally mounted to the high temperature metal sheet material that covers and forms the roof of the industrial oven. A continuous coverage layer is formed of abutting adjacent sheets or tiles and/or overlapping fibrous sheets or tiles. Close spacing is required because any gaps between the sheets could expose the underlying support metal to the high heat of the oven. Thus, sheets of fibrous insulation material that are supported from a flat metal structure can provide a cost effective and simplified oven roof construction compared to the use of refractory brick insulation.
Periodically, through contact, over heating, and/or repeated heat exposure, portions of the fibrous insulation material may become damaged causing exposure of the metal sheet materials supporting the insulation. Continued operation can result in melting of the supporting metal structure and/or complete burn-out of portions of the oven roof. Unfortunately, permanent repairs to damaged portions of the lightweight fibrous insulation material cannot currently be accomplished without shutting down the oven and entering into the oven to provide replacement insulation from within the oven. Discontinuing operation to repair the damage can result in significant product losses, plant downtime and wasted heat energy costs of reheating the oven after it is cooled and repaired. Temporary repairs such as plugging the burned out portion from outside of the oven might keep the operation going; however, such patchwork repair cannot generally prevent continued and increased damage because of the internal exposure of the support structure to the high heat within the oven. Repairs requiring oven shut down can cause costly waste of heat energy, product losses, and costly down time due to interruptions in continuous heat processing of the types typically accomplished using industrial tunnel ovens.